This paper treats the problem of setting the inventory level of closed-loop flow lines operating under the constant-work-in-process (CONWIP) protocol. We solve a huge but simple linear program that models an entire simulation run of a closed-loop flow line in discrete time to determine a production rate estimate of the system. This new approach has been introduced in Helber et al. (2008) for open flow lines with limited buffer capacities. In this paper we present numerical results of the method for closed-loop CONWIP flow lines. The first part of the numerical study deals with the accuracy of the method. In the second part, we focus on the relationship between the CONWIP inventory level and the short-term profit. In our numerical investigation we consider both limited and unlimited local buffer capacities between the machines.